Inductively coupled ballast circuit

ABSTRACT

A ballast circuit is disclosed for inductively providing power to a load. The ballast circuit includes an oscillator, a driver, a switching circuit, a resonant tank circuit and a current sensing circuit. The current sensing circuit provides a current feedback signal to the oscillator that is representative of the current in the resonant tank circuit. The current feedback signal drives the frequency of the ballast circuit causing the ballast circuit to seek resonance. The ballast circuit preferably includes a current limit circuit that is inductively coupled to the resonant tank circuit. The current limit circuit disables the ballast circuit when the current in the ballast circuit exceeds a predetermined threshold or falls outside a predetermined range.

This application is a division of U.S. patent application Ser. No.10/972,169 entitled “Inductively Coupled Ballast Circuit,” filed Oct.22, 2004, now U.S. Pat. 7,180,248; which is a continuation of U.S.patent application Ser. No. 10/246,155 entitled “Inductively CoupledBallast Circuit,” filed Sept. 18, 2002, now U.S. Pat. 6,825,620; whichis a continuation-in-part of U.S. patent application Ser. No. 10/175,095entitled “Fluid Treatment System,” filed Jun. 18, 2002, now U.S. Pat.No. 6,673,250 issued Jan. 6, 2004; which is a continuation-in-part ofU.S. patent application Ser. No. 09/592,194 entitled “Fluid TreatmentSystem,” filed Jun. 12, 2000, now U.S. Pat. No. 6,436,299 issued Aug.20, 2002 which claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application Ser. No. 60/140,159 entitled “WaterTreatment System with an Inductively Coupled Ballast,” filed Jun. 21,1999 and U.S. Provisional Patent Application Ser. No. 60/140,090entitled “Point-of-Use Water Treatment System,” filed Jun. 21, 1999.

This application hereby incorporates by reference U.S. patentapplication Ser. No. 09/596,416 entitled “Point-of-Use Water TreatmentSystem,” filed Jun. 12, 2000, now U.S. Pat. No. 6,451,202 and U.S.patent application Ser. No. 10/133,860 entitled “Inductively PoweredLamp Assembly,” filed Apr. 26, 2002, now U.S. Pat. No. 6,731,071.

FIELD OF THE INVENTION

The present invention generally relates to ballasts and moreparticularly, to an inductively coupled ballast for non-contact powertransfer to a secondary circuit or load.

BACKGROUND OF THE INVENTION

Ballasts are commonly used to supply power to a wide variety ofelectrically powered components. Often ballasts are connected directlyto the component (or load), for example, by “permanent” connections,such as wires or soldered leads on a circuit board, or by “removable”connections, such as plugs or other connectors. Direct electricalconnections present a number of problems. First, direct electricalconnections make it difficult to install and remove the load from theballast. With permanent connections, the electrical leads must besoldered or otherwise secured directly between the ballast and the load.If the ballast or the load is damaged, replacement is complicated by thepermanent connections. Removable connections make separation of theballast and the load easier, but still require some manual manipulation.Removable connectors are also subject to corrosion and may beinadvertently or unintentionally disconnected, for example, byvibrations. Second, in many environments, direct electrical connectionsmust be insulated from the environment to prevent damage to the circuit.For example, in wet environments, exposed electrical connections aresubject to a short circuit. Third, direct electrical connections providea direct and essentially unimpeded path for electricity to flow betweenthe ballast and the load. As a result, power surges and otherpotentially damaging abnormalities in one element can be directlytransfer to the other, thereby permitting problems in one component todamage or even destroy the other.

To address these and other significant problems, there is an increasingtrend to replace conventional direct electrical connections withinductive connections. Inductively coupled systems provide a number ofsignificant advantages over direct connections. First, inductivecouplings do not include permanent or removable physical connectors.Instead, the secondary coil of the load (or secondary circuit) simplyneeds to be placed in the close proximity to the primary coil of theballast. This greatly simplifies installation and removal of the load.Second, the inductive coupling provide a significant level of isolationbetween the ballast and the load. This isolation can protect onecomponent from power surges and other potentially damaging abnormalitiesin the other component.

Unfortunately, conventional inductively coupled ballasts suffer from anumber of problems associated primarily with efficiency. To providemaximum efficiency, it is desirable for the circuit to operate atresonance. Conventional ballasts are designed to operate at resonance bycarefully selecting the components of the ballast in view of the precisecharacteristics of the load. Any variation in the load can move thecircuit dramatically out of resonance. Accordingly, conventionalballasts require very precise selection of the components of the ballastcircuit and secondary circuit. In some applications, the impedance ofthe secondary circuit will vary over time, thereby changing the resonantfrequency of the circuit. For example, in many conventional lightingapplications, the impedance of the lamp will vary as the lamp is heatedand will also vary over the life of the lamp. As a result of thesechanges, the efficiency of conventional, fixed-frequency ballasts willvary over time.

Conventional ballast control circuits employ bipolar transistors andsaturating transformers to provide power. The ballast control circuitsoscillate at frequencies related to the magnetic properties of thematerials and winding arrangements of these transformers. Circuits withsaturating transformer oscillators produce an output in the category ofa square wave, require the transistors of the half bridge to hard-switchunder load and require a separate inductor to limit the current throughthe load. Conventional circuits chop the available power supply voltage,developing voltage spikes at the corners of the square wave as aconsequence of the current limiting inductor. Inductive couplings relyon electromagnetic induction to transfer power from a primary coil to asecondary coil. The amount of current induced in the secondary coil is afunction of the changes in the magnetic field generated by the primarycoil. Accordingly, the amount of current transferred through aninductive coupling is dependent, in part, on the waveform of the currentdriving the primary. A square waveform has relatively small regions ofchange and therefore provides relatively inefficient transfer of power.

These and other deficiencies in prior ballasts are addressed by thepresent invention.

SUMMARY OF THE INVENTION

The present invention discloses an inductively powered ballast circuithaving a current sensing circuit that automatically adjusts thefrequency of the ballast to maintain operation of the ballast at or nearunity power factor.

In one embodiment, the inductively coupled ballast circuit is aself-oscillating half-bridge switching design that operates at highfrequencies. In addition, the inductively coupled ballast circuitself-oscillates partly as a function of the current sensing circuit tomaintain resonance, uses MOSFET transistors as switching elements, andis designed to accommodate an air-core transformer coupling arrangement.

One embodiment of the inductively coupled ballast circuit includes acontrol circuit, an oscillator, a driver, a half-bridge switchingcircuit, and a series resonant tank circuit. The secondary circuitpreferably includes a secondary coil and a load. During operation, thecontrol circuit provides electrical signals to the oscillator, which, inturn, provides electrical signals to direct the driver. The driver thencauses the half-bridge switching circuit to become energized. Thehalf-bridge switching circuit energizes the series resonant tankcircuit, which includes a primary coil. Once the series resonant tankcircuit, and consequently the primary coil, is energized, the secondarycoil becomes inductively energized, thereby providing power to the load.

In one embodiment, the resonant frequency for the inductively coupledballast circuit is about 100 kHz. In addition, the secondary circuitpreferably resonates at about 100 kHz as well. The resonant frequency ofoperation can be adjusted up or down by the control unit to accommodatefor convenient component selection. In addition, selection of theresonant frequency is a function of the component selection in theseries resonant tank and the characteristics of the secondary circuit.

An interesting feature of the inductively coupled ballast circuit is theinductive coupling. The series resonant tank circuit includes aninductive coupler. In one embodiment, the inductive coupler ispositioned adjacent the secondary coil with an air gap therebetween toform an air core transformer. When voltage is applied to the inductivecoupler, magnetic flux in the air gap induces voltage in the secondarycoil thereby energizing the secondary load.

Another interesting feature of the inductively coupled ballast circuitinvolves the air gap of one embodiment. The air gap is the distancebetween the inductive coupler and the secondary coil. The air gap may beselected to provide a current limiting function. In addition, the airgap provides a magnetic flux path for inducing sufficient voltage in thesecondary coil to establish and maintain an operating point for thesecondary load.

Yet another interesting feature involves the frequency of operation ofthe inductively coupled ballast circuit. Both the series resonant tankand the secondary load may be tuned by proper selection of components tooperate at a similar resonant frequency. In addition, impedance matchingbetween the series resonant tank and the secondary load may occur at theresonant frequency. Accordingly, power transfer from the inductivecoupler to the secondary coil may be optimized at a resonant frequencyto maximize power efficiency.

Still another interesting feature involves self-oscillation of theinductively coupled ballast circuit with the oscillator. The oscillatormay include feedback control for monitoring the series resonance tank.The feedback control may allow the oscillator to adjust the frequency tominimize reflected impedance from the secondary circuit. Adjusting thefrequency to maintain resonance minimizes the reflected impedance andmaintains optimum power transfer as the impedance of the secondarycircuit varies.

In another aspect, the present invention preferably includes a currentlimit circuit that monitors the ballast circuit and disables the ballastcircuit if the current to the primary exceeds a desired threshold. Thecurrent limit circuit protects both the load and the ballast circuitfrom excessive current. The current limit circuit is preferably latchedto keep the ballast circuit disabled until reset, for example, by amanual reset switch.

In an alternative embodiment, the current limit circuit may beconfigured to disengage the ballast circuit if the current falls outsideof a desired operating range. This embodiment is particularly useful inapplication where the load may be damaged or function improperly whenoperating under low current.

These and other features and advantages of the invention will becomeapparent upon consideration of the following detailed description of thepresently preferred embodiments of the invention, viewed in conjunctionwith the appended drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a main housing of the water treatmentsystem with its top shroud removed and a filter assembly and theultraviolet lamp assembly removed from the base unit.

FIGS. 2A-C are exploded perspective views of major components of thewater treatment system.

FIG. 3 depicts a block diagram of the major circuits and assemblies ofthe water treatment system.

FIG. 4 depicts a block diagram of the inductively coupled ballastcircuit.

FIG. 5 is an electrical circuit schematic of a portion of theinductively coupled ballast circuit, the ballast feedback circuit andthe interlock circuit.

FIG. 6 depicts the secondary coil, the resonant lamp circuit and theultraviolet lamp of the ultraviolet lamp assembly.

FIG. 7 is an electrical circuit schematic of the starter circuit.

FIG. 8 illustrates an electrical circuit schematic of the radiofrequency identification system used in the water treatment system

FIG. 9 is an electrical circuit schematic of the flow sensor circuit.

FIG. 10 is an electrical circuit schematic of the ambient light sensorcircuit.

FIG. 11 is an electrical circuit schematic of the ultraviolet lightsensor circuit.

FIG. 12 is an electrical circuit schematic of the ambient temperaturesensor circuit.

FIG. 13 is an electrical circuit schematic of the audible generationcircuit.

FIG. 14 is an electrical circuit schematic of the communication port.

FIG. 15 is a plurality of waveforms representing operation of thecurrent sensing circuit.

FIG. 16 is an electrical circuit schematic of the current limit circuit.

FIG. 17 is an electrical circuit schematic of a portion of analternative current feedback circuit.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT OF THE INVENTION

The present invention is directed to an inductively coupled ballastcircuit that is capable of providing power to a wide variety ofelectrically powered components in numerous applications. For purposesof disclosure, embodiments of the ballast circuit will be described inconnection with a water treatment system, and more specifically inconnection with the powering of an ultraviolet lamp in a water treatmentsystem. Although described in connection with this particularapplication, the present invention is well-suited for use in providingpower to other types of lamps, such as incandescent, fluorescent andhalogen lamps used in numerous lighting applications, such as indoor andoutdoor light fixtures, desk lamps, outdoor signage, decorativelighting, automotive lighting, underwater lighting, intrinsically safelighting, and landscape lighting, to name only a few lightingconfigurations and applications. The present invention is also wellsuited for providing power to non-lighting components, such asintegrated battery chargers in various electronic components, includingcell phones, personal digital assistants and the like.

Referring to FIG. 1, the present invention, as used in the illustratedembodiment, discloses an electronic control system for a water treatmentsystem 10 that generally uses carbon-based filters and ultraviolet lightto purify water. In order to appreciate the present invention, it ishelpful to have a general background of the mechanical aspects of watertreatment system 10 for which this illustrated embodiment was intended.Water treatment system 10 includes a main housing 12, a replaceableultraviolet lamp assembly 14 and a filter assembly 16. The ultravioletlamp assembly 14 and the filter assembly 16 are removable andreplaceable from the main housing 12. The main housing 12 includes abottom shroud 18, a back shroud 20, a front shroud 22, a top shroud 24and an inner sleeve shroud 26. A lens 28 accommodates a display 106 (seeFIG. 3) so that information may be displayed about the status of thewater treatment system 10 through the display 106. To assemble the watertreatment system 10, the ultraviolet lamp assembly 14 is securelymounted to the main housing 12 and thereafter the filter assembly 16 ismounted over the ultraviolet lamp assembly 14 and to the main housing12.

As those skilled in the art would recognize, the replaceable ultravioletlamp assembly 14 may be made in such a manner that the ultraviolet lampassembly 14 may not be replaceable. In addition, those skilled in theart would recognize that the replaceable ultraviolet lamp assembly 14may be interchanged with several different types of electromagneticradiation emitting assemblies. As such, the present invention should notbe construed to cover only systems that use ultraviolet lamp assembliesand those skilled in the art should recognize that the disclosure of theultraviolet lamp assembly 14 represents only one embodiment of thepresent invention. Referring to FIGS. 2A-C, the major mechanicalcomponents of the water treatment system 10 are shown in perspectiveview, as relevant to the present invention. As illustrated in FIG. 2A,the inner sleeve shroud 26 includes a plurality of inner sleeve covers30, an inlet valve assembly 32 and an outlet cup assembly 34 with anoutlet cup 36. A bottom shroud assembly 38 is further disclosed thatincludes the bottom shroud 18 along with an inlet assembly 40 and anoutlet assembly 42. An electronics assembly 44 fits securely in thebottom shroud 18, the details of which will be set forth below indetail. These components are securely mounted to the bottom shroud 18,the back shroud 20, the front shroud 22, the top shroud 24, the innersleeve shroud 26 and the lens 28 when the water treatment system 10 isfully assembled. A magnet holder 46 and a magnet 48 are also housed inthe top shroud 24 in the illustrated embodiment.

Referring to FIG. 2B, the ultraviolet lamp assembly 14 generallyincludes a base subassembly 50, a secondary coil 52, a bottom supportsubassembly 54, a top support assembly 56, a pair of quartz sleeves 58,an ultraviolet lamp 60, an O-ring 62 and a pair of cooperating enclosurereflector subassemblies 64. Generally speaking, the secondary coil 52,the bottom support subassembly 54 and the enclosure reflectorsubassemblies 64 are connected with the base subassembly 50. Theenclosure reflector subassemblies 64 house the pair of quartz tubes 58,the ultraviolet lamp 60 and the O-ring 62. The top support assembly 56fits securely over the top of the enclosure reflector assemblies 64 whenthe ultraviolet lamp assembly 14 is fully assembled.

As illustrated in FIG. 2C, the filter assembly 16 generally includes abase assembly 66, a filter block assembly 68, a filter housing 70 and anelastomeric filter-housing grip 72. Generally speaking, the filter blockassembly 68 fits over the base assembly 66 which, in turn, isencapsulated by the filter housing 70. The filter housing grip 72 fitsover the top of the filter housing 70, thereby providing a better gripfor removing the filter housing 70. The filter assembly 16 filters aflow of water by directing the flow through the filter block assembly 68before being directed to the ultraviolet lamp assembly 14.

FIG. 3 illustrates an electronic control system 100 for the watertreatment system 10 generally described above. In the illustratedembodiment, the water treatment system 10 is controlled by a controlunit 102, which is preferably a microprocessor. As illustrated in FIG.4, the control unit 102 is electrically connected with the inductivelycoupled ballast circuit 103 of the present invention. The ballastcircuit 103 includes the ultraviolet lamp assembly 14 and electronicassembly 44, which are inductively coupled as illustrated by the dottedline in FIG. 4. This control unit 102 is also electrically connected tothe ultraviolet lamp assembly 14 through two-way wireless communication,as will be set forth in greater detail below. During operation, thecontrol unit 102 is capable of generating a predetermined electricsignal that is directed to the inductively coupled ballast circuit 103,which instantaneously energizes the lamp assembly 14 which, in turn,provides high-intensity ultraviolet light that treats the flow of water.

In the illustrated embodiment, the control unit 102 is also electricallyconnected with a flow sensor circuit 104, a display 106, an ambientlight sensor circuit 108, a visible light sensor circuit 110, a powerdetection circuit 112, an ambient temperature sensor circuit 114, anaudio generation circuit 116, a memory storage device 118, acommunications port 120, a ballast feedback circuit 122 and a radiofrequency identification system 124. As further illustrated in FIG. 3,an ultraviolet light radio frequency identification transponder 126 isconnected with the ultraviolet lamp assembly 14 and a filter radiofrequency identification transponder 128 is connected with the filterassembly 16. The ultraviolet radio frequency identification transponder126 and the filter radio frequency identification transponder 128communicate with the radio frequency identification system 124 usingtwo-way wireless communication, as will be set forth in greater detailbelow.

Generally speaking, the flow sensor circuit 104 is used by the controlunit 102 to determine when water or fluid is flowing and to keep trackof the volume of water or fluid that is being processed by the watertreatment system 10. The display 106 is driven by the control unit 102and is used to display information about the status of the watertreatment system 10. Several different types of displays are known inthe art and may be used in the present invention; however, the preferreddisplay is a vacuum florescent display. The ambient light sensor circuit108 measures the amount of ambient light and, in turn, provideselectrical signals to the control unit 102 so that it can adjust theintensity of the display 106 accordingly.

The visible light sensor circuit 110 provides the control unit 102 withelectrical signals related to the intensity level of the light that isbeing emitted by the ultraviolet lamp assembly 14. This is importantbecause these signals allow the control unit 102 to increase or decreasethe intensity of the electromagnetic radiation being emitted by theultraviolet lamp assembly 14. Those skilled in the art would recognizethat the visible light sensor circuit 110 may be interchanged withvarious electromagnetic radiation sensor circuits that are capable ofsensing the intensity of electromagnetic radiation that is emitted fromvarious electromagnetic radiation emitting devices that may be used inthe present invention.

The power detection circuit 112 provides the control unit 102 withelectrical signals that indicate the presence or absence of power to thewater treatment system 10. Power is provided to the water treatmentsystem 10 from an external power source, such as a conventional poweroutlet. Those skilled in the art would recognize that several circuitsexist that monitor external power sources and provide correspondingelectrical signals in response to losses of power.

The ambient temperature sensor circuit 114 measures the ambienttemperature of the atmosphere so that the water treatment system 10 canmaintain a temperature level above freezing or some other predeterminedtemperature setting. The control unit 102 can energize the ultravioletlamp 60 to generate heat if necessary. The audio generation circuit 116is used by the control unit 102 to generate audible enunciations. Theaudible enunciations typically occur during predetermined system statesthat are experienced by the water treatment system 10. Thesepredetermined system states are recognized by the control unit 102which, in turn, activates the audio generation circuit 116 to create theaudible enunciation.

As previously set forth, the memory storage device 118 is alsoelectrically connected with the control unit 102. The memory storagedevice 118 is used to store various data values related to the watertreatment system 10 and its related components. In the illustratedembodiment, the memory storage device 118 is an EEPROM or some otherequivalent storage device. Those skilled in the art would recognize thatvarious memory storage devices are available that could be used in thepresent invention.

The communications port 120 is also electrically connected with thecontrol unit 102, which provides the water treatment system 10 with theability to conduct bidirectional communication between the control unit102 and a peripheral device, such as a personal computer or hand-heldmonitoring device. In the illustrated embodiment, the communicationsport 120 uses the RS-232 communication platform to communicate with theperipheral device. The communications port 120 may also be connectedwith the ultraviolet lamp assembly 14 and the filter assembly 16 tomonitor and control various operational characteristics of these devicesin other embodiments. However, in the illustrated embodiment, the radiofrequency identification system 124 is used to report information to thecontrol unit 102 about the ultraviolet lamp assembly 14 and the filterassembly 16.

In the embodiment depicted in FIG. 3, the radio frequency identificationsystem 124 uses signals from the ultraviolet light radio frequencyidentification transponder 126 and the filter radio frequencyidentification transponder 128 to report various information to thecontrol unit 102. During operation, the ultraviolet light radiofrequency identification transponder 126 and the filter radio frequencyidentification transponder 128 communicate with the radio frequencyidentification system 124 using wireless communication. Since theultraviolet lamp assembly 14 and the filter assembly 16 are designed tobe replaceable at the end of its useful life, each ultraviolet lampassembly 14 and filter assembly 16 contains a transponder 126, 128 thatstores information specific to each device. Those skilled in the artwould recognize that the ultraviolet light radio frequency transpondercould be used in conjunction with other electromagnetic radiationemitting devices or assemblies. The radio frequency identificationsystem 124 is set forth in greater detail below.

Referring to FIG. 4, in the illustrated embodiment of the invention, theultraviolet lamp assembly 14 is energized by the inductively coupledballast circuit 103 that is electrically connected with the control unit102. In the illustrated embodiment, the inductively coupled ballastcircuit 103 is a self-oscillating, half-bridge switching design thatoperates at high frequencies. The inductively coupled ballast circuit103 self-oscillates once resonance is achieved, uses MOSFET transistorsas switching elements, and is designed to accommodate an air-coretransformer coupling arrangement, which simplifies the design of theultraviolet lamp assembly 14. The ultraviolet lamp assembly 14 or otherelectromagnetic radiation emitting assemblies may be readily replacedbecause of the air-core transformer coupling arrangement created by theinductively coupled ballast circuit 103.

As illustrated in FIG. 4, the inductively coupled ballast circuit 103 ofthe described embodiment generally includes a control circuit 142, anoscillator 144, a driver 146, a half-bridge switching circuit 148, and aseries resonant tank circuit 150. The ultraviolet lamp assembly 14generally includes the secondary coil 52 (see FIG. 2), a resonant lampcircuit 152 and the ultraviolet lamp 60. The oscillator 144 iselectrically connected with the control unit 102, which energizes theoscillator 144 by providing electric signals to the control circuit 142.During operation, the oscillator 144 provides electrical signals todirect the driver 146, which then causes the half-bridge switchingcircuit 148 to become energized. The half-bridge switching circuit 148energizes the series resonant tank circuit 150 that, in turn,inductively energizes the ultraviolet lamp 60 in the ultraviolet lampassembly 14.

As noted above and as further illustrated in FIG. 4, the ultravioletlamp assembly 14 includes the secondary coil 52, the resonant lampcircuit 152 and the ultraviolet lamp 60 while the electronic assembly 44houses the control circuit 142, the oscillator 144, the driver 146, thehalf-bridge switching circuit 148 and the series resonant tank circuit150. As previously set forth, once the series resonant tank circuit 150is energized, the secondary coil 52 in the ultraviolet lamp assembly 14becomes inductively energized as illustrated by the dotted line in FIG.4. In the illustrated embodiment, the resonant frequency for the ballastcircuit 103 is about 100 kHz. In addition, the ultraviolet lamp assembly14 resonates at about 100 kHz as well. The frequency of operation may bevaried to maintain resonance of the series resonant tank circuit 150 andthe ultraviolet lamp assembly 14 as discussed in detail below. As knownto those skilled in the art, the resonant frequency may be any desiredfrequency selected as a function of the component selection in theseries resonant tank circuit 150 and the ultraviolet lamp assembly 14.

Referring to FIG. 5, the control circuit 142 is electrically connectedwith the control unit 102 and the oscillator 144. The control circuit142 includes a plurality of resistors 156, 158, 160, 162, 164, 166, aplurality of capacitors 168, 170 172, a diode 174, a first operationalamplifier 176 and a second operational amplifier 178. As illustrated,resistor 156 is connected with a first direct current (“DC”) powersource 180, the output of the control unit 102 and resistor 158.Resistor 158 is further connected with diode 174, resistor 160 andcapacitor 168. The first DC power source 180 is connected with capacitor168, which is also connected with diode 174. Diode 174 is furtherconnected with a ground connection 182, as those skilled in the artwould recognize. Resistor 160 is connected with the negative input ofoperational amplifier 176 and the positive input of operationalamplifier 178 to complete the current path from the control unit 102 tothe operational amplifiers 176, 178.

Referring once again to the control circuit 142 depicted in FIG. 5,resistor 162 is connected with a second DC power source 184 and inseries with resistors 164 and 166. Resistor 166 is connected with theground connection 182 and capacitor 170, which is, in turn, connectedwith the first DC power source 180 and resistor 164. The positive inputof operational amplifier 176 is electrically connected between resistors162 and 164, which provides a DC reference voltage to operationalamplifier 176 during operation. The negative input of operationalamplifier 178 is electrically connected between resistors 164 and 166,which provides a DC reference voltage to operational amplifier 178during operation. The output of operational amplifiers 176 and 178 isconnected with the oscillator 144, as set forth in detail below.

During operation, the control circuit 142 turns the oscillator 144 onand off based on input from the control circuit 102 and the magneticinterlock sensor 192, as described in more detail below. The controlcircuit 142 receives electrical signals from the control unit 102 and,in turn, acts as a window comparator that only switches the oscillator144 on when the input voltage produced by the control unit 102 is withina certain voltage window. The preferred signal from the control unit 102is an AC signal that, together with its duty cycle, allows the controlunit 102 to turn the ultraviolet lamp 60 on and off through theremaining components of the inductively coupled ballast circuit 103, aswill be set forth below. The control circuit 142 also prevents falsetriggering and allows positive control if the control unit 102 fails.

As illustrated in FIG. 5, the first DC power source 180 and the secondDC power source 184 provide power to the circuits depicted in FIG. 5.Those skilled in the art of electronics would recognize that DC powersupply circuits are well known in the art and beyond the scope of thepresent invention. For the purposes of the present invention, it isimportant to note that such circuits exist and are capable of beingdesigned to produce various DC voltage values from a given AC or DCpower source. In the illustrated embodiment, a +14VDC and a +19VDCsignal is used, as indicated throughout the figures. Those skilled inthe art would recognize that the circuits disclosed in FIG. 5 could bedesigned to operate on different DC voltage levels and that these valuesshould not be construed as a limitation on the present invention. Inanother embodiment, 300VDC is used to supply power to the half-bridgeswitching circuit 148 to optimize power transfer.

In the embodiment depicted in FIG. 5, the output of the control circuit142 is connected with an interlock circuit 190 to prevent theultraviolet lamp 60 from becoming energized if the water treatmentsystem 10 is not properly assembled. The interlock circuit 190 includesa magnetic interlock sensor 192, a plurality of resistors 193, 194, 196,198, 200, 202, 204, a transistor 206 and a diode 208. Referring to FIG.1, in the illustrated embodiment, the magnetic interlock sensor 192 ispositioned so that if the top shroud 24 is not securely positioned onthe inner sleeve shroud 26, the water treatment system 10 will notenergize the ultraviolet lamp 60. However, those skilled in the artwould recognize that the magnetic interlock sensor 192 may be placed inother convenient places of the water treatment system 10 as well.

Referring to FIG. 5, the magnetic interlock circuit 190 operates bydirecting the output of the control circuit 142 to the ground connection182, through transistor 206, if the magnetic interlock sensor 192detects that the water treatment system 10 is not assembled properly, asset forth above. As those skilled in the art would recognize, if thewater treatment system 10 is not assembled properly, the output of themagnetic interlock sensor 192 causes the current flowing throughresistors 194, 196 and 198 to energize the gate of transistor 206, whichthereby shorts the output signal of the control circuit 142 to theground connection 182. The magnetic interlock sensor 192 is powered bythe second DC power source 184 through resistor 193 and is alsoconnected with the ground connection 182. In addition, the magneticinterlock sensor 192 sends a signal to the control unit 102, through thecombination of resistors 200, 202 and 204, diode 208, first DC powersource 180 and second DC power source 184. This signal also allows thecontrol unit 102 to determine when the water treatment assembly 10 isnot assembled properly. To that end, the interlock circuit 190 providestwo methods of ensuring that the ultraviolet lamp 60 is not energized ifthe water treatment system 10 is not assembled properly. The magneticinterlock is not necessary for the operation of the present invention.

Referring once again to FIG. 5, the oscillator 144 provides electricalsignals that energize the driver 146 while the water treatment system 10is treating a flow of water. The oscillator 144 begins operatingimmediately once an electrical signal is sent from the control unit 102,through control circuit 142, as set forth above. As readily apparent,the oscillator 144 may also be controlled by any other mechanism capableof activating and deactivating the oscillator 144. The illustratedoscillator 144 comprises an operational amplifier 210, a linear biasresistor 212, a buffer circuit 214, a buffer feedback protect circuit216 and a current sensing circuit 218. During operation, the operationalamplifier 210 receives input signals from the control circuit 142, thelinear bias resistor 212 and the current sensing circuit 218. Theoperational amplifier 210 is also connected with the second DC powersource 184 and the ground connection 182, which energizes theoperational amplifier 210.

As illustrated in FIG. 5, the illustrated buffer circuit 214 comprises afirst transistor 220, a second transistor 222 and a pair of resistors224, 226. The output of operational amplifier 210 is connected with thegates of transistors 220, 222, thereby controlling operation oftransistors 220, 222. The second DC power source 184 is connected withresistor 224, which is also connected with collector of transistor 220.The emitter of transistor 220 is connected with resistor 226, theemitter of transistor 222 and the input of the driver 146. The collectorof transistor 222 is connected with ground connection 182. Duringoperation, the buffer circuit 214 buffers the output signal from theoperational amplifier 210 and prevents load changes from pulling thefrequency of oscillation. In addition, the buffer circuit 214 increasesthe effective gain of the inductively coupled ballast circuit 103, whichhelps ensure a quick start of the oscillator 144.

The buffer feedback protect circuit 216 comprises a pair of diodes 228,230 that are electrically connected with the output of the buffercircuit 214 by resistor 226. As illustrated in FIG. 5, the second DCpower source 184 is connected with the cathode of diode 228. The anodeof diode 228 and the cathode of diode 220 are connected with resistor226 and the linear bias resistor 212. The linear bias resistor 212provides bias feedback signals to the negative input of operationalamplifier 210. In addition, the anode of diode 230 is connected withground connection 182, which completes the buffer feedback protectcircuit 216. The buffer feedback circuit 216 protects the buffer circuit214 from drain to gate Miller-effect feedback during operation of thewater treatment system 10.

As illustrated in FIG. 5, the current sensing circuit 218 includes afirst multi-winding transformer 232, a plurality of resistors 234, 236,238, a pair of diodes 240, 242, and a capacitor 244. The transformer 232preferably includes a primary having two windings that are connected inparallel between the output of the half-bridge switching circuit 148 andthe input of the series resonant tank circuit 150 as illustrated in FIG.5. The transformer 232 preferably includes a primary with two windingsconnected in parallel rather than a single winding to reduce the totalreactance on the primary side of the transformer, thereby reducing thereactive impact of the transformer 232 on the tank circuit 150. In otherapplications, the primary side of the transformer may be divided into adifferent number of windings. For example, the transformer 232 mayinclude only a single winding where reduction of the reactive impact ofthe transformer is not important or may include three or more windingswhere even further reduction of the reactive impact of the transformer232 is desired.

The first lead of the secondary coil of transformer 232 is electricallyconnected with resistors 234, 236, 238, the diodes 240, 242 and thepositive input of the operational amplifier 210. The second lead of thesecondary coil of the transformer 232 is connected with resistor 238,the cathode of diode 242, the anode of diode 240 and capacitor 244. Assuch, resistor 238 and diodes 242, 244 are connected in parallel withthe secondary winding of transformer 232, as illustrated in FIG. 5.Capacitor 244 is also electrically connected with the negative input ofoperational amplifier 210. In addition, resistor 234 is connected withthe second DC power source 184 and resistor 236 is connected with theground connection 182. Resistors 234, 236 and 238 protect theoperational amplifier 210 from current overload and diodes 240, 242 clipthe feedback signal that is sent to the input of the operationalamplifier 210.

During operation, the oscillator 144 receives signals from the controlcircuit 142 that charge capacitor 244, which, in turn, sends anelectrical signal to the negative input of the operational amplifier210. The output of the operational amplifier 210 is electricallyconnected to the driver 146 through the buffer circuit 214. As describedin more detail below, the driver 146 energizes the half-bridge switchingcircuit 148, which in turn provides power to the tank circuit 150ultimately powering inductive coupler 270. As illustrated in FIG. 5, thetransformer 232 is connected in the current path between the half-bridgeswitching circuit 148 and the tank circuit 150. The transformer 232sends electrical signals back through resistors 234, 236 and 238, whichlimit the current, to the inputs of the operational amplifier 210 toprovide a current sensing feedback. As described in more detail below,the current sensing feedback provided by transformer 232 allows theoscillator 144 to self-resonate despite changes in the load. Theinductively coupled ballast circuit 103 remains oscillating until thecontrol unit 102 shuts the water treatment system 10 down or transistor206 of the interlock circuit 190 pulls the input to the oscillator 144low.

More specifically, the current sensing circuit 218 provides feedback tothe operational amplifier 210 that controls the timing of the oscillator144 so that the oscillator 144 does not impair the tank circuit's 150inherent tendency to oscillate at resonant frequency. In general, thecurrent in the series resonant tank circuit 150 flows through theprimary coils of transformer 232, thereby inducing a voltage in thesecondary coil of transformer 232. The AC signal generated by thetransformer 232 is superimposed upon a DC reference voltage set byresistors 234 and 236. The operational amplifier 210 is preferably aconventional difference operational amplifier providing an output based,in part, on the difference between the amplitude of the signal on thepositive lead and the amplitude of the signal of the negative.Accordingly, the output of the operational amplifier 210 oscillatesabove and below the reference voltage in accordance with the oscillatingsignal of the current feedback circuit. The operational amplifier 210 ispreferably alternately driven between saturation and cutoff, therebyproviding a quasi-square wave output. When the output of the operationalamplifier 210 exceeds the reference signal, transistor 220 is driven to“on,” while transistor 222 is driven to “off,” thereby chargingcapacitor 248 and discharging capacitor 250. When the output of theoperational amplifier 210 falls below the reference signal, transistor222 is driven to “on” while transistor 220 is driven to “off,” therebydischarging capacitor 248 and charging capacitor 250. This alternatingcharging/discharging of capacitors 248 and 250 results in an alternatingsignal being applied to the primary coil of the driver 146, as describedin more detail below. The frequency shifting (or resonance seeking)operation of the circuit is described in more detail with reference toFIG. 15. In this illustration, the current in the inductive coupler 270is represented by waveform 600, the voltage in the current transformer232 is represented by waveform 602 and the current feedback signal isrepresented by waveform 604 (shown without clipping of diodes 240 and242). As noted above, the operational amplifier 210 is alternatelydriven between saturation and cutoff with a transition period interposedbetween the saturation and cutoff portions of the waveform. The lengthof the transition period is dictated by the slope of the currentfeedback signal. The timing of the operational amplifier 210 isdependent on the length of the transition period. By varying the lengthof the transition period, the timing of the transitions in theoperational amplifier 210 output signal is controlled. This shift intiming is perpetuated through the driver 146 and half-bridge switchingcircuit 148 having the affect of varying the frequency and also possiblythe amplitude of the signal in the tank circuit 150. The altered signalin the tank circuit 150 is reflected into the current feedback signal bythe current transformer 232 to perpetuate the frequency shift. When theload on the secondary coil 52 increases, a corresponding increase occursin the amplitude of the current in the tank circuit 150. This increasedsignal is represented by waveform 606 in FIG. 15. The increased signalin the tank circuit 150 results in a corresponding increase in thevoltage in the current transformer 232. The increased voltage in thecurrent transformer 232 is represented by waveform 608. The increasedvoltage in the current transformer 232 finally results in an increase inthe amplitude of the current feedback signal, represented by waveform610 (shown without clipping of diodes 240 and 242). The increasedcurrent feedback signal has a greater slope at the zero crossings andtherefore causes the operational amplifier 210 to transition from onestate to the other sooner in time. This in turn causes the transistors220 and 222 to switch sooner in time and the AC signal applied to thedriver 146 to alternate sooner in time. Ultimately, there is acorresponding shift in the timing of the signals applied to the tankcircuit 150 by the half-bridge switching circuit 148. The shift intiming of the signals applied by the half-bridge switching circuit 148has the effect of increasing the frequency and possibly the amplitude ofthe inherent oscillating signal in the tank circuit 150, therebyshifting, or “truncating,” the timing of the signal in the tank circuit150. The truncated signal in the tank circuit 150 is reflected into thecurrent sensing circuit 218. This varies the current feedback signalapplied to the operational amplifier 210, thereby perpetuating thefrequency shift and effecting an increase in the frequency of theoscillator. In this way the oscillator 144 and driver 146 permit thetank circuit 150 to shift its frequency to remain at resonance despite achange in load. When the load on the secondary coil 52 decreases, thefrequency of the oscillator 144 decreases in a manner essentiallyopposite that described above in connection with an increase infrequency. In summary, the decreased load results in decreased currentin the tank circuit 150. This results, in turn, in a decrease in thevoltage induced in the current transformer 232 and a decrease in theamplitude of the current feedback signal. The decreased current feedbacksignal has a decreased slope, and accordingly causes the operationalamplifier 210 to complete the transition between saturation and cutofflater in time. The transistors 220 and 222 also transition later intime, thereby shifting the timing of the driver 146 and the timing ofthe switching circuit 148. The net effect of the shift in the timing ofthe switching circuit 148 is to shift, or “extend”, the frequency andpossibly vary the amplitude of the signal in the tank circuit 150. Theextended signal is reflected into the current sensing circuit 218 whereit is returned to the operational amplifier 210 to perpetuate thedecrease in frequency of the oscillator 144. Optimal performance isachieved when the half-bridge switching circuit 148 alternates at thezero crossings of the current signal in the tank circuit 150. Thisprovides optimal timing of the energy supplied by the switching circuit148 to the tank circuit 150. In some applications, it may be necessaryor desirable to shift the phase of the current feedback signal toprovide the desired timing. For example, in some applications, theparasitic effect of the various circuit components may result in a shiftin the phase of the current feedback signal. In such applications, thecurrent sensing circuit can be provided with components, such as an RCcircuit, to shift the signal back into alignment so that the switchingcircuit 148 alternates at the zero crossings. FIG. 17 illustrates aportion of an alternative current sensing circuit 218′, which includesan RC circuit configured to shift the phase of the current feedbacksignal 120 degrees. In this embodiment, the current sensing circuit 218′is essentially identical to the current sensing circuit 218 of the abovedescribed embodiment, except that it includes two capacitors 800, 802and two resistors 804, 806 that are connected along the leads extendingback to the operation amplifier 210. FIG. 17 further illustrates thatthe secondary of the current transformer 232 can be connected to ground182 to provide a zero reference, if desired. If the current transformer232 is connected to ground 182, resistor 238 is eliminated.

Referring once again to FIG. 5, the output of the oscillator 144 iselectrically connected with the driver 146. In the illustratedembodiment, the driver 146 is a multi-winding transformer that providespower to the half-bridge switching circuit 148. Transformer 246 is thepreferred driver 146 in the illustrated embodiment because the phasingarrangement of the transformer 246 insures that the half-bridgeswitching circuit 148 will be alternately driven, which avoids crossconduction. A double arrangement of capacitors 248, 250 is electricallyconnected with the primary winding of transformer 246, therebypreventing DC current saturation in the transformer 246. Capacitor 246is also connected with the ground connection 182 and capacitor 250 isalso connected with the second DC power source 184.

The transformer 246 includes two secondary coils that are electricallyconnected to opposite legs of the half-bridge switching circuit 148 sothat the half-bridge switching circuit 148 receives energy fromtransformer 246. The half-bridge switching circuit 148, which is alsoillustrated in FIG. 5, is electrically arranged as a MOSFET totem polehalf-bridge switching circuit 252 that is driven by both secondary coilsof transformer 246. The MOSFET totem pole half-bridge switching circuit252 includes a first MOSFET transistor 254 and a second MOSFETtransistor 256 that provide advantages over conventional bipolartransistor switching circuits. Energy is transferred from the driver 146to the MOSFET transistors 254, 256 through a plurality of resistors 258,260, 262, 264. The MOSFET transistors 254, 256 are designed tosoft-switch at zero current and exhibit only conduction losses duringoperation. The output generated by MOSFET transistors 254, 256 is morein the form of a sine wave that has fewer harmonics than that generatedby traditional bipolar transistors. Using MOSFET transistors 254, 256also provides advantages by reducing radio frequency interference thatis generated by the MOSFET transistors 254, 256 while switching duringoperation.

In the half-bridge switching circuit 148 depicted in FIG. 5, the firstsecondary coil of transformer 246 is connected with resistor 258 andresistor 260. The second secondary coil of transformer 246 is connectedwith resistor 262 and resistor 264. Resistor 260 is connected with thegate of MOSFET transistor 254 and resistor 264 is connected with thegate of MOSFET transistor 256. As illustrated, the first secondary coilof transformer 246 and resistor 258 are connected with the source ofMOSFET transistor 254. The second secondary coil of transformer 246 andresistor 264 are connected with the gate of MOSFET transistor 256. Thedrain of MOSFET transistor 254 is connected with the second DC powersource 184 and the source of MOSFET transistor 254 is connected with thedrain of MOSFET transistor 256. The source of MOSFET transistor 256 andresistor 262 are connected with the ground connection 182.

A further benefit of the driver 146 is that multi-winding transformer246 is a very convenient way to apply gate drive voltage to the MOSFETtransistors 254, 256 that exceeds the second DC power source 184. TheMOSFET transistors 254, 256 provide further advantages because they havediodes inherent in their design that protect the MOSFET totem polehalf-bridge switching circuit 252 from load transients. In addition,over-voltages reflected from the series resonant tank circuit 150, bychanges in load, are returned to supply rails by the inherent diodeswithin MOSFET transistors 254, 256.

Referring to FIG. 5, the output of the half-bridge switching circuit 148is connected with the input of the series resonant tank circuit 150,which, in turn, inductively energizes the secondary coil 52 of theultraviolet lamp assembly 14 (FIG. 4). As set forth above, in theillustrated embodiment of the invention, the current sensing circuit 218of the oscillator 144 is connected with the output of the half-bridgeswitching circuit 148 and the input of the series resonant tank circuit150 to provide current sense feedback to operational amplifier 210 ofthe oscillator 144 during operation. The primary coil of the transformer232 is connected in series between the output of the half-bridgeswitching circuit 148 and the input of the series resonant tank circuit150 as illustrated in FIG. 5.

Referring to FIG. 5, the series resonant tank circuit 150 comprises aninductive coupler 270, the parallel combination of a pair of tankcapacitors 271, 272, a pair of diodes 274, 276 and a capacitor 278. Theinductive coupler 270 is connected to the primary coil of transformer232 and tank capacitors 271, 272. Tank capacitor 271 is also connectedwith the second DC power source 184 and tank capacitor 272 is alsoconnected with the ground connection 182. In addition, tank capacitor271 and the second DC power source 184 are connected with the anode ofdiode 274. The cathode of diode 274 and capacitor 278 are both connectedwith the second DC power source 184. Capacitor 278 is connected with theanode of diode 276 and the ground connection 182. Tank capacitor 272 isalso connected the cathode of diode 276.

The series resonant tank circuit 150 sees all of the stray inductancesof the component combination of the inductively coupled ballast circuit103. This is relevant because the stray inductance, which is thecombined inductance seen by the series resonant tank circuit 150, willlimit the power transfer to the load (the ultraviolet light assembly 14)if its precludes the system from operating outside of resonance. Theinductance of the secondary coil 52 and the resonant lamp circuit 152are also reflected impedance values that help determine and limit thepower that is delivered to the secondary coil 52 of the ultraviolet lampassembly 14. In general, brute force oscillator/transformer combinationshave power transfer limits because of stray and reflected inductance. Inother words, the inductance of transformers and capacitors appears inseries with the load thereby limiting power transfer capability.

In the illustrated embodiment, the frequency of operation for the seriesresonant tank circuit 150 is set near 100 KHz, which is determined bythe inductance of the inductive coupler 270 and the parallel capacitancevalue of tank capacitors 271, 272, which are 0.1 μF capacitors in theillustrated embodiment. Tank capacitors 271, 272 must have lowdissipation factors and be able to handle high levels of current, whichis about 14 amps at start up. This resonant frequency may be adjusted upor down and has been selected only for convenient component selections.As noted above, the ballast circuit 103 seeks resonance through afeedback signal from the current sensing circuit 218. The currentfeedback signal is proportional to the current in the resonant tankcircuit 150. The range of frequencies through which the ballast circuit103 can search for resonance are readily varied by adjusting the valuesof the tank capacitors 271, 272. For example, by increasing the value ofthe tank capacitors 271, 272, the range can generally be decreased.

The inductive coupler 270 of the illustrated embodiment includes 10turns of wire to generate the power required to inductively energize thesecondary coil 52 in the ultraviolet lamp assembly 14. The inductivecoupler 270 is preferably positioned in the outlet cup 36 (see FIG. 2A)of the water treatment system 10 and wire is wrapped around the outletcup 36 in a diameter of about 3.5 inches. In the illustrated embodiment,litz wire is used for the inductive coupler 270 because litz wire isespecially efficient in both performance and operating temperature, dueto a skin effect caused by operating at 100 kHz. As set forth above, theinductive coupler 270 inductively energizes the secondary coil 52 of theultraviolet lamp assembly unit 14 during operation.

Referring to FIG. 2A, the secondary coil 52 of the ultraviolet lampassembly unit 14 is positioned in the outlet cup 36 and the inner sleeveshroud 26 when the water treatment system 10 is assembled. In theillustrated embodiment, the secondary coil 52 has 55 turns of smalldiameter wire that is wrapped around the secondary coil 52 in a diameterof about two inches. It is important to note that the coupling betweenthe outlet cup 36 and the base subassembly 50, which houses thesecondary coil 52, is designed to be very tolerant of gaps andmisalignment. In fact, gaps are used to adjust the coupling coefficient,thereby adjusting the operating point of the ultraviolet lamp 60.

The permeance of the air gap between the inductive coupler 270 and thesecondary coil 52 may be adjusted by changing the distance between theinductive coupler 270 and the secondary coil 52, as known in the art. Asis apparent, the air gap within the air core transformer formed with theinductive coupler 270 and the secondary coil 52 may be selectivelyadjusted to limit power transfer from the inductive coupler 270 to thesecondary coil 52. In addition, selective adjustment of the air gap mayadjust the control response of the oscillator 144. Accordingly,selection of the permeance of the air gap balances overcurrentprotection of the inductively coupled ballast circuit 103 with thebandwidth and responsiveness of the oscillator 144 when the secondarycoil 52 is inductively energized.

As known in the art, inductive energization of the secondary coil 52occurs when the inductive coupler 270 induces a magnetic flux in the airgap between the secondary coil 52 and the inductive coupler 270. In theillustrated embodiments, the magnetic flux is an alternating flux with afrequency that is preferably controlled by the oscillator 144 in aneffort to maintain resonance.

During operation, the oscillator 144 may control the frequency at closeto the resonant frequency of the series resonant tank circuit 150 andthe ultraviolet lamp assembly unit 14. As previously discussed, thecurrent sensing circuit 218 monitors the reflected impedance in theseries resonance tank circuit 150 to allow the inductively coupledballast circuit 103 to self-oscillate to a frequency which optimizespower transfer efficiency. If, for example, the impedance reflected bythe ultraviolet light assembly 14 to the series resonant tank circuit150 shifts slightly, the current sensing circuit 218 may adjust thefrequency to correct for the shift in power transfer efficiency.

In the case where the impedance shifts significantly lower, such as, forexample, when the ultraviolet lamp 60 fails in a shorted condition, theincrease in current is limited by the air gap. As known in the art, theair gap functions to limit the amount of impedance that may bereflected. In addition, the impedance that is reflected may result in animpedance mismatch causing the reflection of power back to the seriesresonant tank circuit 150. As is readily apparent, the reflection ofpower to the series resonance tank circuit 150 may further limit powertransfer to the secondary coil 52. Based on the combination of the airgap and the resonant frequency control, the inductively coupled ballastcircuit 103 may be optimized for efficient operation while maintainingdesirable levels of overcurrent protection.

The configuration of the air core transformer provides for simple andefficient replacement of the ultraviolet light assembly 14. In addition,the present invention provides further advantages by providing acoupling that does not require special contacts for the ultraviolet lampassembly 14 because of the inductively coupled ballast circuit 103.Further, the configuration eliminates the need for conductors or othersimilar power transfer mechanism that may compromise waterproofing,corrode and/or otherwise malfunction.

As readily apparent to those skilled in the art, the inductively coupledballast circuit 103 set forth above may be readily incorporated intoother lighting systems or other systems requiring the transmission ofelectric power, and provides advantages over prior art ballast circuitsbecause it drives lamps and other loads without requiring a physicalconnection and because it seeks resonance with the secondary. Theinductively coupled ballast circuit 103 is also capable ofinstantaneously energizing several different styles of lamps, bulbs andother loads.

Referring once again to FIG. 5, the ballast feedback circuit 122 iselectrically connected with the inductive coupler 270 of the seriesresonant tank circuit 150 and the control unit 102. The ballast feedbackcircuit 122 provides feedback to the control unit 102 while theinductively coupled ballast circuit 103 is driving the ultraviolet lamp60. This allows the control unit 102 to monitor the energy beingprovided by the inductive coupler 270 to the secondary coil 52 of theultraviolet lamp assembly 14. This provides the control unit 102 withthe ability to determine if the ultraviolet lamp 60 is on or off andalso, in other embodiments, the amount of current and voltage beingapplied to the ultraviolet lamp 60.

As depicted in FIG. 5, the ballast feedback circuit 122 includes anoperational amplifier 280, a pair of resistors 282, 284, a pair ofdiodes 286, 288 and a capacitor 290. The signal from the series resonanttank circuit 150 is directed to the anode of diode 286. The cathode ofdiode 286 is connected with capacitor 290 and resistor 282. In addition,resistor 282 is connected with the anode of diode 288, resistor 284 andthe positive input of operational amplifier 280. Resistor 284 is alsoconnected with the positive input of operational amplifier 280 and thefirst DC power source 180. Capacitor 290 is also connected with thefirst DC power source 180, while the cathode of diode 288 is connectedwith the second DC power source 184. The negative input of operationalamplifier 280 is connected directly with the output of operationalamplifier 280. The output of operational amplifier 280 is connected withthe control unit 102, thereby providing the feedback signal fromoperational amplifier 280 to the control unit 102.

Referring to FIG. 6, the ultraviolet lamp assembly 14 of one embodimentincludes the ultraviolet lamp 60, the resonant lamp circuit 152 and thesecondary coil 52. The ultraviolet lamp 60 of the illustrated embodimentcomprises a pair of bulbs 300, 302 and a pair of filaments 304, 306. Thebulbs 300, 302 are held together with an upper connection bracket 308and a lower connection bracket 310. The secondary coil 52 is connectedwith the resonant lamp circuit 152, which, in turn, is connected withthe filaments 304, 306 of the ultraviolet lamp 60. The resonant lampcircuit 152 comprises a capacitor 312 that is electrically connected inseries with the bulbs 300, 302 and a starter circuit 314 as illustrated.

Although an ultraviolet lamp assembly 14 is set forth in the illustratedembodiment of the present invention, as previously set forth, thoseskilled in the art would recognize that present invention is well-suitedfor use with other electromagnetic radiation emitting assemblies orlight sources. For example, the ultraviolet lamp assembly 14 may use apulsed white light lamp or a dielectric barrier discharge lamp todeactivate microorganisms in the flow of water. Those skilled in the artwould recognize that the inductively coupled ballast circuit 103 may beused to drive not only various types of electromagnetic radiationemitting devices, but also other loads that might benefit from thewireless power supply or resonance-seeking characteristic of the presentinvention. As such, the present invention should not be limited to watertreatment systems or lamps assemblies, but instead should be broadlyinterpreted to encompass a wide variety of power supply applications.

As illustrated in FIG. 7, the starter circuit 314 comprises a bridgerectifier circuit 320, a silicon-controlled rectifier 322, a seriesarrangement of diodes 324, 326, 328, 330, a triac 332, a plurality oftransistors 334, 336, a plurality of resistors 338, 340, 342, 344, 346and a plurality of capacitors 348, 350. As those skilled in the artwould recognize, the triac 332 may be any equivalent device, such as aFET transistor or a silicon controlled rectifier. In addition, thoseskilled in the art would recognize that the bridge rectifier circuit 320comprises a plurality of diodes 352, 354, 356, 358 that are connectedwith the filaments 304, 306 of the ultraviolet lamp 60.

Referring to FIG. 7, the bridge rectifier circuit 320 is connected withsilicon-controlled rectifier 322, resistor 338 and the ground connection182. Silicon-controlled rectifier 322 is also connected with the seriesarrangement of diodes 324, 326, 328, 330 and the triac 332, which areboth also connected with the ground connector 182. Resistor 338 isconnected with triac 332, resistor 340 and resistor 342. Resistor 340 isconnected with the collector of transistor 334, the base of transistor336, capacitor 348 and resistor 344. Capacitor 348 and resistor 344 arefurther connected with the ground connection 182. Resistor 342 isconnected with the emitter of transistor 336 and capacitor 350, which isalso connected with the ground connection 182. The gate of triac 332 isconnected with the emitter of transistor 334. The collector oftransistor 336 is connected with the base of transistor 334 and resistor346. Resistor 346 is connected with the ground connection 182 tocomplete the starter circuit 314.

Referring back to FIG. 6, during operation, capacitor 312 limits thecurrent supplied to the ultraviolet lamp 60 from the secondary coil 52by changing the reflected impedance of the ultraviolet lamp 60 throughthe inductive coupler 270 (see FIG. 5) of the series resonant tankcircuit 150. As is apparent, by selecting the value of capacitor 312 inview of the impedance of the ultraviolet lamp 60 and the secondary coil52, the ultraviolet lamp assembly 14 may be impedance matched with thepower source (the series tank circuit 150). In addition, the ultravioletlamp assembly 14 may be tuned to resonate at a frequency similar to theresonant frequency of the series resonant tank circuit 150, therebyoptimizing coupling and minimizing reflected power.

The starter circuit 314 is designed to short filaments 304, 306 duringstart-up, thereby causing maximum preheat of the bulbs 300, 302. Thisallows the ultraviolet lamp 60 to strike maximum dispersion of themercury in bulbs 300, 302, thereby causing maximum intensity anddelivering the highest dose of ultraviolet light to the water as itpasses through the ultraviolet lamp assembly 14. In other words, thestarter circuit 314 is designed so that the ultraviolet lamp 60instantly turns on at maximum intensity. The placement of mercury inbulbs 300, 302 is important for maximum output. When the mercurycondenses within the plasma path, the mercury is dispensed more evenlythroughout bulbs 300, 302. The faster dispersion also allows quickerpeak intensity, thereby providing the ability to give the flow of watera faster, more intense dose of ultraviolet light at start-up. As isapparent, the shorting of the starter circuit 314 allows maximum powertransfer while maintaining optimum power transfer efficiency sinceimpedance matching remains in place. It is further apparent from theforegoing discussion that the air gap functions to provide currentlimiting during startup while still providing sufficient power transferto the secondary coil to almost instantly start the ultraviolet light 60at maximum intensity.

Referring to FIG. 2B, the O-ring 62 acts as a heat sink and ispurposefully placed between the path of water, which flows through thepair of quartz tubes 58, and the ultraviolet lamp 60 plasma path toallow the mercury to condense within the plasma path for improvedinstant ultraviolet light output. Referring again to FIG. 6, as theultraviolet lamp 60 is energized, the full-circuit voltage potential isapplied across capacitor 312, filaments 304, 306 and the starter circuit314. Because of the low impedance value of the filaments 304, 306 andthe starter circuit 314, which acts as a short at start-up, the currentis high for maximum preheat of the ultraviolet lamp 60. This causes thepreheat of the ultraviolet lamp 60 to disperse some initial mercury atstart-up. When the starter circuit 314 heats up, the starter circuit 314RC time constant releases the shorting device, which is the triac 332(FIG. 7) in one embodiment, thereby providing full voltage across thefilaments 304, 306. In other embodiments, the shorting device may beother mechanisms such as, for example, electro-magnetically controlledreed switches, an optically controlled triac and/or any other devicecapable of moving between a contacting and non-contacting state. Inaddition, the shorting device may be controlled by an external controlmechanism such as, for example, electromagnet control signals, radiofrequency control signals, optical control signals or any othermechanism capable of communicating some form of signal to the shortingdevice absent conductors therebetween. The starter circuit 314 allows abetter start than a thermister because thermisters consume more energyafter opening and do not open as quickly. In addition, as is apparent,operation of the starter circuit 314 occurs in a stand-alone fashionwithout external control wires or other features that may compromisewater tightness and/or replacement ability of the ultraviolet lightassembly 14.

Referring to FIG. 8, one radio frequency identification system 124 isillustrated electrically connected with the control unit 102. The radiofrequency identification system 124 uses a base station to communicatewith the ultraviolet light radio frequency identification transponder126 and the filter radio frequency identification transponder 128. Theradio frequency identification system 124 allows contactless reading andwriting of data, which is transmitted bidirectionally between the basestation 360 and the transponders 126, 128. In one embodiment, the radiofrequency identification system 124 is manufactured by TEMICSemiconductors under model number TR5551A-PP.

The radio identification system 124 is used by the control unit 102 tokeep track of information specific to each ultraviolet lamp assembly 14and filter assembly 16. As previously set forth, the ultraviolet lampassembly 14 and the filter assembly 16 are both designed to be readilyreplaceable. Since the ultraviolet light radio frequency identificationtransponder 126 and the filter radio frequency transponder 128 arelocated in the ultraviolet lamp assembly 14 or the filter assembly 16,these devices are never separated, which allows the control unit 102 toread and write information to and from the transponders 126, 128 throughthe base station 360.

Referring once again to FIG. 8, the ultraviolet light radio frequencyidentification transponder 126 includes a transponder antenna 362 and aread/write IDIC® (e5551) chip 364. The read/write IDIC® (e5551) chipfurther includes an EEPROM device 366 that physically stores therelevant information for each respective ultraviolet lamp assembly 14 inmemory locations. In the illustrated embodiment, the informationconsists of an ultraviolet lamp serial number, ultraviolet lamp startlimit, ultraviolet lamp on-time limit, ultraviolet lamp install timelimit, ultraviolet lamp cycle on-time, cycle mode low temperature,minimum ultraviolet lamp on-time, ultraviolet lamp high-mode time andultraviolet lamp preheat time. In addition, the EEPROM device 366 in theultraviolet light radio frequency identification transponder 126 allowsthe control unit 102 to keep track of ultraviolet lamp install time,ultraviolet lamp powered time, ultraviolet lamp starts and totalultraviolet lamp cold starts.

The ultraviolet lamp serial number is unique to each ultraviolet lampassembly 14 and allows the control unit 102 of the water treatmentsystem 10 to keep track of which ultraviolet lamp assemblies 14 havebeen installed in the water treatment system 10. The ultraviolet lampstart limit relates to the maximum allowed number of ultraviolet lampstarts and the ultraviolet lamp on-time limit relates to the maximumallowed installation time for the ultraviolet lamp 60. The ultravioletlamp install time limit relates to the maximum allowable installationtime for the ultraviolet lamp assembly 14 and the ultraviolet lamp cycleon-time relates to the minimum amount of time the ultraviolet lamp 60needs to be energized in low-temperature mode. The cycle modelow-temperature information relates to the temperature value to whichthe water treatment system 10 switches to low-temperature mode and theminimum ultraviolet lamp on-time relates to the minimum amount of timethe ultraviolet lamp 60 must remain energized. The ultraviolet lamphigh-mode time information relates to the amount of time the ultravioletlamp 60 operates in high mode and the ultraviolet lamp preheat timerelates to the amount of time the ultraviolet lamp 60 needs to bepreheated.

As previously set forth, the EEPROM device 366 in the ultraviolet lightradio frequency identification transponder 126 is also capable ofkeeping track of the ultraviolet lamp install time. This informationtracks the number of hours that the current ultraviolet lamp 60 has beenplugged into the water treatment system 10. In one embodiment, for everyminute the ultraviolet lamp 60 is plugged into the water treatmentsystem 10, one minute is added to the total. The EEPROM device 366 alsokeeps track of the ultraviolet lamp powered time and the totalultraviolet lamp powered time. The ultraviolet lamp powered time and thetotal ultraviolet lamp powered time keeps track of the amount of timethe ultraviolet lamp 60 has been on so that the control unit 102 candetermine if a new ultraviolet lamp assembly 14 needs installed. Theultraviolet lamp starts memory location stores the number of times theultraviolet lamp 60 has been started, so that the control unit 102 canuse this information to determine the end of life of the ultravioletlamp 60. The total ultraviolet lamp cold-starts memory location tracksthe number of times the ultraviolet lamp 60 has been started when theambient temperature sensor 114 indicates that the temperature is below apredetermined threshold value.

Referring once again to FIG. 8, the filter radio frequencyidentification transponder 128 includes a transponder antenna 368 and aread/write IDIC® (e5551) chip 370. The read/write IDIC® (e5551) chip 370further includes an EEPROM device 372 that physically stores therelevant information for each respective filter assembly 16 in memorylocations. In the described embodiment, the relevant informationconsists of a filter assembly serial number, a filter assembly volumelimit, a filter assembly install time limit, and a plugged filterassembly threshold percent.

The filter assembly serial number is used for unique identification ofdifferent filter assemblies 16 so that the control unit 102 can monitorwhich filter assemblies 16 have been installed in the water treatmentsystem 10. The filter assembly volume limit is associated with thevolume of water the filter assembly is designed to filter beforereaching the end of its useful life. The filter assembly install timelimit is used by the control unit 102 to compute the remaining life ofthe filter assembly 16 based on a predetermined allowable wet time. Theplugged filter assembly threshold percent contains the maximum allowablepercentage of flow reduction for the filter assembly 16 before it needsreplaced. This maintains the percent of degradation of the filterassembly 16 before a plugged filter assembly 16 error is initiated bythe control unit 102.

The radio frequency identification system 124 includes the base station360, a coil 380, a plurality of diodes 382, 384, 386, 388, 390, 392,394, a plurality of resistors 396, 398, 400, 402, 404, 406, 408, 410,412, 414, 416, 418, 420 and a plurality of capacitors 422, 424, 426,428, 430, 432, 434, 436 that are electrically connected as illustratedin FIG. 8. Those skilled in the art would recognize that the connectionof the aforementioned components is well known to those skilled in theart. The radio frequency identification system 124 has been installed inthe water treatment system 10 using specifications set forth for theTK5551A-PP, which, as previously set forth, is manufactured by TEMICSemiconductors. For the purpose of the present invention, it isimportant to note that the base station 360 uses the coil 380 forbidirectional communication with the ultraviolet light radio frequencyidentification transponder 126 and the filter radio frequencyidentification transponder 128.

The control unit 102 is electrically connected with the base station 360so that the control unit 102 can communicate with the base station 360.As such, the control unit 102 is capable of reading and writinginformation to and from the ultraviolet light radio frequencyidentification transponder 126 and the filter radio frequencyidentification transponder 128 through the base station 360 by using thecoil 380. The radio frequency identification system 124 is connectedwith the first DC power source 180 and the second DC power source 184 asillustrated in FIG. 8, which provides the radio frequency identificationsystem 124 with energy to function during operation.

Those skilled in the art would recognize that other identificationsystems could be used with the present invention, such as contact-typeidentification systems. However, the illustrated embodiment of theinvention uses a radio frequency identification system 124 because ofthe inherent benefits such a system provides.

Referring to FIG. 9, the flow sensor circuit 104 is connected with thecontrol unit 102 to provide electrical signals to the control unit 102indicating that water is flowing through the water treatment system 10.The flow sensor circuit 104 includes a flow sensor 440, a plurality ofcapacitors 442, 444 and a resistor 446. The flow sensor is manufacturedby Allegro under model number 3134. Capacitor 442 is connected with theflow sensor 440, the first DC power source 180 and the second DC powersource 184. The output of the flow sensor 440 is connected with theparallel combination of resistor 446 and capacitor 444, before beingconnected with the control unit 102. Resistor 446 and capacitor 444 arealso connected with the second DC power source 184. During operation,the flow sensor 440 delivers electrical signals to the control unit 102,which indicates that water is flowing in the water treatment system 10,thereby causing the control unit 102 to instantaneously energize theultraviolet lamp 60. Those skilled in the art would recognize thatseveral variations exist on the disclosed flow sensor circuit 104 andthat the disclosed flow sensor circuit 104 is provided by way of exampleonly and should be not construed as a limitation of the presentinvention.

Referring to FIG. 10, the ambient light sensor circuit 108 comprises aphotosensitive diode 450, an operational amplifier 452, a plurality ofresistors 454, 456, 458, 460, a diode 462 and a capacitor 464electrically connected as illustrated. For purposes of the presentinvention, it is sufficient to note that the photosensitive diode 450provides electrical signals to the negative input of the operationalamplifier 452, which, in turn, conditions the signal for the controlunit 102. The ambient light sensor circuit 108 is powered by the firstDC power source 180 and the second DC power source 184. 10. Thoseskilled in the art would recognize that several variations exist on thedesign of ambient light sensor circuits 108 and that the illustratedembodiment should not be construed as a limitation on the presentinvention.

Referring to FIG. 11, as previously set forth, the visible light sensorcircuit 110 is connected with the control unit 102 to provide electricalsignals to the control unit 102 corresponding to the intensity of theultraviolet lamp 60 during operation. In one embodiment, the visiblelight sensor circuit 110 comprises a photosensitive resistor 470, anoperational amplifier 472, a diode 474, a plurality of resistors 476,478, 480, 482, 484, 486 and a capacitor 488 electrically connected asdepicted in FIG. 11. In addition, the visible light sensor circuit 110is powered by the first DC power source 180 and the second DC powersource 184. Those skilled in the art would recognize that the visiblelight sensor circuit 110 takes the electrical signal generated by thephotosensitive resistor 470 and amplifies it with the operationalamplifier 472, before being directed to the control unit 102. Further,those skilled in the art would recognize that the design of visiblelight sensor circuits 110 can vary and that the disclosed ultravioletlight sensor circuit 110 is by way of example only and should not beconstrued as a limitation of the present invention.

Referring to FIG. 12, as previously set forth, one ambient temperaturesensor circuit 114 is connected with the control unit 102 to provide thecontrol unit 102 with electrical signals that change with correspondingchanges in the ambient temperature. The ambient temperature sensorcircuit 114 comprises a thermistor 490, an operational amplifier 492, aplurality of resistors 494, 496, 498 and a capacitor 500 that areelectrically connected as illustrated in FIG. 12. During operation, thevoltage drop across thermistor 490 changes as the ambient temperaturechanges, thereby causing the electrical signal that is sent from theoutput of the operational amplifier 492 to the control unit 102 toeither increase or decrease. Those skilled in the art would recognizethat the design of ambient temperature sensor circuits 114 can vary. Oneambient temperature sensor circuit 114 illustrated in FIG. 12 is by wayof example only and should not be construed as a limitation of thepresent invention.

Referring to FIG. 13, as previously set forth, one audio generationcircuit 116 is connected with the control unit 102 for generatingaudible enunciations in response to predetermined system states. Oneaudio generation circuit 116 comprises a piezoelectric element 510, aplurality of transistors 512, 514, 516, a plurality of resistors 518,520, 522, 524, 526, 528, 530, 532, 534, a plurality of capacitors 536,538 and a diode 540, which are electrically connected as depicted inFIG. 13. As readily apparent to those skilled in the art, the controlunit 102 is capable of energizing the piezoelectric element 510, therebycausing the piezoelectric element 510 to generate audible tones throughvibrations. Those skilled in the art would recognize that severaldevices and circuits exist that are capable of generating audible tones.The presently disclosed audio generation circuit 116 is by way ofexample only and likewise should not be construed as a limitation of thepresent invention.

Referring to FIG. 14, as previously set forth, the communications port120 is connected with the control unit 102. The communications port 120is used by the control unit 102 to communicate bidirectionally with aperipheral device (not shown), such as a personal computer or ahand-held device. In one embodiment, the communications port 120comprises a plurality of zenar diodes 550, 552, 554 and a plurality ofresistors 556, 558, 560, 562, 562, 566, 568, 570, which are electricallyconnected as illustrated in FIG. 14. The first DC power source 180 andthe second DC power source 184 provide power to the communications port120. The communications port 120 is designed to use the RS-232communications standard, as well known in the art. A port connector 572is provided so that the peripheral device can be connected with thecommunications port 120. Those skilled in the art would recognize thatdifferent types of communication ports may be used and are beyond thescope of the present invention. To that end, one communications port 120disclosed herein is by way of example only and should not be construedas a limitation of the present invention.

In one embodiment, the ballast circuit 103 also includes a current limitcircuit 700 designed to monitor the current produce by the circuit, andshut the circuit down when it falls outside of desired parameters. Thecurrent limit circuit 700 can be configured to disable the ballastcircuit 103 when a current threshold is exceeded (i.e. an upper limit)or when the current falls outside of a range (i.e. both upper and lowerlimits). Upper and lower limits are particularly useful in applicationswhere low current and unstable operation can damage the load, forexample, in lighting applications where a dimming function is achievedby increasing the air gap between the primary coil and the secondarycoil.

One embodiment of the current limit circuit 700 is shown in FIG. 16. Thecurrent limit circuit 700 includes a current sensing transformer 702that produces current proportional to the flow of current to the primarycoil 270. The current transformer 702 is preferably created by forming acoil of wire around the core of the current sensing transformer 232 ofthe current sensing circuit 218. The current from the currenttransformer 702 develops a voltage across resistor 704. Another resistor706 is tied to the input voltage of ballast circuit. The relationship tothe input voltage causes the level to shift as the input voltage shifts.This permits the current transformer 702 to track the real performanceeven as input voltage shifts. Resistor 708 allows a voltage bias fromground that helps to raise the variable current transformer voltage to alevel detectable by the operational amplifier 710. Resistors 712 isconnected between voltage source 184 and the positive input ofoperational amplifier 710. Resistor 714 is connected between groundconnection 182 and the positive input of operational amplifier 710.Resistors 712 and 714 establish a limit or threshold to set theoperating and non-operating modes. Resistor 716 is connected between thecurrent transformer 70 and the negative input lead of operationalamplifier 710 to prevent the operational amplifier 710 from drawing toomuch current from the current transformer 102. The output of theoperational amplifier 702 is connected to integrated circuit 720, whichis preferably a conventional latch or flip-flop, such as IC 14044. Whenthe output from the operational amplifier 702 is driven high, the latchis triggered, thereby latching the disable signal. The integratedcircuit 720 preferably maintains the ballast circuit103 in the disabledcondition until the manual reset switch 722 is pressed or otherwiseactuated. Alternatively, the reset switch 722 can be replaced by a timercircuit (not shown) that resets the current limit circuit 700 after adefined period of time. The current limit circuit 700 may also include atest circuit 724 that permits testing of the operation of the currentlimit circuit 700. The test circuit 724 is connected to power source 184and includes resistor 726 and switch 728. When switch 728 is depressedor otherwise actuated, current in excess of the threshold is applied tothe operational amplifier 710. If operating properly, this current willcause the current limit circuit 700 to disable the ballast circuit 103.

As an alternative, the current from the current transformer 702 can bemonitored by a microprocessor that is programmed to disable the ballastcircuit when the current exceeds the desired threshold or falls outsideof the desired range. In some applications, however, the microprocessormay not provide sufficient speed to provide acceptable response times.Accordingly, the hardware embodiment described may be preferable in someapplication.

While the invention has been described in its currently best known modesof operation and embodiments, other modes and embodiments of theinvention will be apparent to those skilled in the art and arecontemplated. In addition, although one embodiment of the presentinvention is directed to a water treatment system 10, those skilled inthe art would recognize that the present invention may be readilyincorporated in several different types of fluid treatment systems.

1. A ballast circuit comprising: a primary subcircuit having a primarycoil; a current sensor connected to said primary subcircuit, saidcurrent sensor sensing a characteristic of a current in said primarysubcircuit; a control circuit supplying current to said primary coil,said control circuit varying a characteristic of the current supplied tosaid primary coil as a function of said characteristic sensed by saidcurrent sensor; a secondary coil inductively coupled with said primarycoil, wherein said primary coil inductively energizes said secondarycoil; a load electrically connected to said secondary coil, wherebypower is provided to said load by said secondary coil; and an oscillatorincluding a buffer circuit that prevents load changes from pulling thefrequency of oscillation of said oscillator.
 2. A ballast circuitcomprising: a primary subcircuit having a primary coil; a current sensorconnected to said primary subcircuit, said current sensor sensing acharacteristic of a current in said primary subcircuit; a controlcircuit supplying current to said primary coil, said control circuitvarying a characteristic of the current supplied to said primary coil asa function of said characteristic sensed by said current sensor; asecondary coil inductively coupled with said primary coil, wherein saidprimary coil inductively energizes said secondary coil; a loadelectrically connected to said secondary coil, whereby power is providedto said load by said secondary coil; and a driver including amulti-winding transformer.
 3. A ballast circuit comprising: a primarysubcircuit having a primary coil; a current sensor connected to saidprimary subcircuit, said current sensor sensing a characteristic of acurrent in said primary subcircuit; a control circuit supplying currentto said primary coil, said control circuit varying a characteristic ofthe current supplied to said primary coil as a function of saidcharacteristic sensed by said current sensor; a secondary coilinductively coupled with said primary coil, wherein said primary coilinductively energizes said secondary coil; a load electrically connectedto said secondary coil, whereby power is provided to said load by saidsecondary coil; and a half-bridge switching circuit including a MOSFETtotem pole half bridge switching circuit.
 4. A ballast circuitcomprising: a primary subcircuit having a primary coil; a current sensorconnected to said primary subcircuit, said current sensor sensing acharacteristic of a current in said primary subcircuit; a controlcircuit supplying current to said primary coil, said control circuitvarying a characteristic of the current supplied to said primary coil asa function of said characteristic sensed by said current sensor; asecondary coil inductively coupled with said primary coil, wherein saidprimary coil inductively energizes said secondary coil; and a resonantlamp circuit electrically connected to said secondary coil, wherebypower is provided to said resonant lamp circuit by said secondary coil,wherein said primary coil is disposed in a series resonant tank circuit,said resonant lamp circuit and said series resonant tank circuitresonating at about the same frequency, and further wherein said seriesresonant tank circuit includes a pair of tank capacitors, a pair ofdiodes and a capacitor.
 5. A ballast circuit comprising: a primarysubcircuit having a primary coil; a current sensor connected to saidprimary subcircuit, said current sensor sensing a characteristic of acurrent in said primary subcircuit; a control circuit supplying currentto said primary coil, said control circuit varying a characteristic ofthe current supplied to said primary coil as a function of saidcharacteristic sensed by said current sensor; a secondary coilinductively coupled with said primary coil, wherein said primary coilinductively energizes said secondary coil; and a resonant lamp circuitelectrically connected to said secondary coil, whereby power is providedto said resonant lamp circuit by said secondary coil, wherein saidresonant lamp circuit comprises a capacitor and a starter circuit.
 6. Aninductive coupling comprising: a primary circuit having: a subcircuitcontaining a primary coil, a sensor for sensing a characteristic ofpower in said subcircuit, and a control circuit means for supplyingpower to said primary coil, said control circuit means varying acharacteristic of the power supplied to said primary coil as a functionof said characteristic sensed by said sensor; and a secondary circuithaving: a secondary coil inductively coupled with said primary coil,wherein said primary coil inductively energizes said secondary coil, anda load electrically connected to said secondary coil, whereby power isprovided to said load by said secondary coil, the sensed characteristicis affected by a reflected impedance of said secondary circuit.
 7. Aninductive coupling comprising: a primary circuit having: a subcircuitcontaining a primary coil, a sensor for sensing a characteristic ofpower in said subcircuit, and a control circuit means for supplyingpower to said primary coil, said control circuit means varying acharacteristic of the power supplied to said primary coil as a functionof said characteristic sensed by said sensor, said varied characteristicof said power supplied to said primary coil comprises a frequency of avoltage applied to said primary coil; and a secondary circuit having: asecondary coil inductively coupled with said primary coil, wherein saidprimary coil inductively energizes said secondary coil, and a loadelectrically connected to said secondary coil, whereby power is providedto said load by said secondary coil, wherein the sensed characteristicis affected by a reflected impedance of said secondary circuit.